Soil and site information for the design selection and design of all systems is the same. The quantity and quality of the information needed of the various pieces of information depends on the site and the field interpretation of the site evaluator. Information defining soil adequate to accept, transfer and treat the wastewater is needed for the volume soil to become the defined soil component.

Although there is considerable discussion of site evaluation to assess the treatment capacity of soil, little is actually done with the data. The retention time needed for the reduction of organisms, determination of anaerobic zones for estimating denitrification or evaluating the soil phosphorus adsorption capacity is seldom considered. Seldom if ever are the oxygen transport capabilities of the site evaluated. More interpretations for treatment could be done using information currently collected if the treatment goals were better defined.

Most interpretations of site evaluation are to size the infiltration surface. The porosity of the soil and the potential for soil clogging combine to control wastewater infiltration. Site evaluations usually provide the texture, structure and other factors controlling soil porosity as well as the quality of the wastewater to estimate the clogging potential. System geometry to maximize the use of soil oxygen is seldom considered. Based on these estimates, design loading or infiltration rates are estimated. Once infiltrated the wastewater continues to move from the system. Estimates of the rate the wastewater exits the site have been made based on the porosity of the soil, the depth of soil and the slope. The information needed for linear loading rates are currently collected by the site evaluator and sometimes used by the designer.

Please address any questions to Dr. David Lindbo.

This page created by
Roland O. Coburn, Research Technician I on 1/10/03.